POLY(3-HYDROXYBUTYRATE) DEPOLYMERASES BIND TO THEIR SUBSTRATE BY A C-TERMINAL LOCATED SUBSTRATE-BINDING SITE

Binding of (i) purified wild-type poly(3-hydroxybutyrate) (PHB) depoly merase PhaZ4 of Pseudomonas lemoignei, (ii) a purified truncated form of PhaZ4, which lacked 55 C-terminal amino acids and (iii) commercial lactate dehydrogenase to aqueous suspensions of PHB, chitin or cellulo se was studied. Only the wild-type PHB depolymerase was specifically a ble to bind to PHB granules. No other combination of protein and polym eric substrate resulted in polymer-bound protein. Similar results were obtained for other PHB depolymerases. We concluded that the C-termina l amino acids of PHB depolymerases represent a PHB-specific binding do main or at least an essential part of it.